1. Field of the Invention
The present invention relates to an object detecting system for detecting an object by transmitting an electromagnetic wave such as laser and the like toward the object and receiving a reflected wave from the object.
2. Description of the Related Art
FIG. 9 shows a prior art object detecting system mounted in a vehicle for detecting the position of a vehicle traveling ahead of the vehicle with the detection system (which will be referred to as a preceding vehicle hereinafter), and the distance between the vehicle and the preceding vehicle. A vertically elongated transmitted beam B is reciprocally moved laterally with its lateral width limited, by reflecting a laser beam transmitted by a laser diode LD, from a mirror M reciprocally turned about a rotational axis S. A reflected wave R resulting from the reflection of the transmitted beam from an object is caught in a fixed receiving area and received by a photodiode PD. The distance from the vehicle to the object can be detected, based on the time lapsed from the transmission of the beam B to the reception of the reflected wave R, and the direction of the object can be detected, based on the direction of the transmitted beam B at that time.
The transmitted beam from such object detecting system is transmitted through a glass surface G for protecting the laser and mirror from dust and water. However, when an ice crystal is deposited on the glass surface G contacting with open air, as shown in FIG. 10, the crystal acts as a prism to divert a portion of the transmitted beam in a different direction, whereby the original transmitted beam and a ghost beam weaker than the original transmitted beam, may be transmitted simultaneously in some cases. As a result, there is a possibility that a reflected wave resulting from the reflection of the transmitted beam from the object and a reflected wave resulting from the reflection of the ghost beam from the object are received in the photodiode, whereby a non-existing virtual image is detected in addition to the original object.
Suppose that an object to be detected exists in front of a vehicle and there is a ghost beam generated and offset leftwards from the transmitted beam by an angle 2, as shown in FIGS. 11A and 11B. In this case, when a reflected wave resulting from the reflection of the beam transmitted toward the front of the vehicle, is received in the course of movement of the transmitted beam and the ghost beam in a direction of an arrow a from the left to the right, an object existing in front of the vehicle is detected (see FIG. 11A). When the ghost beam is then transmitted toward the front of the vehicle with a slight time lag, the reflected wave resulting from the reflection of the ghost beam from the object is received. At this time, the transmitted beam faces rightwards at the angle 2 from the front and moreover, the object detecting system recognizes the direction of the object as the direction of the transmitted beam. For this reason, the virtual image of the object is detected on the right from the front of the vehicle by the reflected wave of the ghost beam (see FIG. 11B). As a result, although, in fact, only a single object exists in front of the vehicle, the two objects are misdetected as if they exist in front of the vehicle and on the right from the front of the vehicle, respectively.
Further, there is a possibility that the ghost beam is generated not only when an ice crystal has been deposited on the glass surface G, but also when the glass surface G has been flawed and when a transparent seal has been affixed onto the glass surface G.
Accordingly, it is an object of the present invention to prevent the misdetection of an object due to a ghost beam.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided an object detecting system for detecting the presence of an object by transmitting an electromagnetic wave and receiving a reflected wave resulting from the reflection of the electromagnetic wave from the object, comprising an object recognizing means for recognizing an object, based on the result of the reception of the reflected wave, and a virtual image determining means for determining a virtual image of the object, based on a comparison of a plurality of results of the recognition provided by the object recognizing means.
With the above arrangement, the object is recognized based on the result of the reception of the reflected wave of the electromagnetic wave transmitted toward the object, and hence, the virtual image due to the ghost beam can be determined based on the comparison of the plurality of results of the recognition. Therefore, a virtual image can be prevented from being misdetected as an actually existing object.
According to a second aspect and feature of the present invention, the object detecting system further includes a virtual image deleting means for deleting the object determined as the virtual image by the virtual image determining means, from the results of the recognition provided by the object recognizing means.
With the above arrangement, the object determined as the virtual image is deleted from the results of the recognition, provided by the object recognizing means and therefore, only the actually existing object including no virtual image, can be detected correctly.
According to a third aspect and feature of the present invention, there is provided an object detecting system for detecting the presence of an object by transmitting an electromagnetic wave and receiving a reflected wave resulting from the reflection of the electromagnetic wave from the object, comprising a first discriminating means for discriminating an object having a reflected wave with a reception level equal to or larger than a first reference level, a second discriminating means for discriminating an object which existing at a distance equal to the distance to the object, discriminated by the first discriminating means and having a reflected wave with a reception level equal to or smaller than a second reference level, and a virtual image determining means for determining the object discriminated by the second discriminating means is a virtual image of the object discriminated by the first discriminating means.
With the above arrangement, an object having a reflected wave with a reception level equal to or larger than the first reference level, is recognized as an actually existing object, and an object existing at a distance equal to the distance to the actually existing object and having a reflected wave with a reception level equal to or smaller than the second reference level, is recognized as a virtual image of the actually existing object. Therefore, it is possible to reliably discriminate the actually existing object and the virtual image thereby prevent the occurrence of the misdetection.
According to a fourth aspect and feature of the present invention, the first reference level of the first discriminating means is set larger than the second reference level of the second discriminating means.
With the above arrangement, the first reference level is set larger than the second reference level and hence, it prevents misdetection of an actual existing object as a virtual image and misdetection of a virtual image as an actual existing object.
According to a fifth aspect and feature of the present invention, the first reference level of the first discriminating means is set such that it is smaller as the distance to an object is larger.
With the above arrangement, the first reference level is set such that it is smaller as the distance to an object is larger and therefore, an accurate determination can be achieved in consideration of attenuation of the reflected wave, with an increase in distance to an object.
According to a sixth aspect and feature of the present invention, the second reference level of the second discriminating means, is set such that it is smaller as the distance to an object is larger.
With the above arrangement, the second reference level is set such that it is smaller, as the distance to an object is larger and therefore, an accurate determination can be achieved in consideration of the attenuation of the reflected wave, with an increase in distance to an object.
According to a seventh aspect and feature of the present invention, the virtual image determining means conducts the determination for an object, when the distance to the object is shorter than a predetermined value.
With the above arrangement, the virtual image determining means conducts the determination of a virtual image only for an object when the distance to the object is shorter than a predetermined value. Therefore, it is possible to prevent the low-accuracy determination of a virtual image by a reflected wave of an originally weak ghost beam for an actual weak object existing farther away.
According to an eighth aspect and feature of the present invention, there is provided an object detecting system for detecting the presence of an object by transmitting an electromagnetic wave and receiving a reflected wave resulting from the reflection of the electromagnetic wave from the object, comprising a first discriminating means for discriminating an object having a reflected wave with a reception level equal to or larger than a first reference level, a third discriminating means for discriminating an object existing at a distance equal to the distance to the object discriminated by the first discriminating means and having a reflected wave with a reception level smaller than the reception level of the object by a predetermined value or more, and a virtual image determining means for determining the object discriminated by the third discriminating means is a virtual image of the object discriminated by the first discriminating means.
With the above arrangement, an object having a reflected wave with a reception level equal to or larger than the first reference level is discriminated as an actual existing object, and an object existing at a distance equivalent to the distance to the actual existing object and having a reflected wave with a reception level smaller than the reception level of the actual existing object by a predetermined value or more, is discriminated as a virtual image of the actual existing object. Therefore, it is possible to reliably discriminate the actual existing object and the virtual image to prevent the occurrence of a misdetection.
According to a ninth aspect and feature of the present invention, there is provided an object detecting system for detecting the presence of an object by transmitting an electromagnetic wave and receiving a reflected wave resulting from the reflection of the electromagnetic wave from the object: comprising a first discriminating means for discriminating an object having a reflected wave with a reception level equal to or larger than a first reference level, a second discriminating means for discriminating an object existing at a distance equal to the distance to the object discriminated by the first discriminating means and having a reflected wave with a reception level smaller than the reception level of the object discriminated by the first discriminating means by a second predetermined value and with a reception level equal to or smaller than a second reference level, and a virtual image determining means for determining the object discriminated by the second discriminating means as a virtual image of the object discriminated by the first discriminating means.
With the above arrangement, an object having a reflected wave with a reception level equal to or larger than the first reference level is recognized as a actual existing object, and an object existing at a distance equal to the distance to the actual existing object and providing a reflected wave with a reception level smaller than the reception level of the actual existing object by the second predetermined level and equal to or smaller than the second reception level, is recognized as a virtual image of the actual existing object. Therefore, it is possible to reliably discriminate the actual existing object and the virtual image to prevent the occurrence of the misdetection.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.